Intradermal injections are used for delivering a variety of substances. Many of these substances have proven to be more effectively absorbed into or react with the immune response system of the body when injected intradermally. Recently, clinical trials have shown that hepatitis B vaccines administered intradermally are more immunogenic if administered intramuscularly. In addition, substances have been injected intradermally for diagnostic testing, such as, for example using what is known in the art as the “Mantoux test” to determine the immunity status of the animal against tuberculosis and the immediate hypersensitivity status of Type I allergic diseases.
An intradermal injection is made by delivering the substance into the epidermis and upper layers of the dermis. Below the dermis layer is subcutaneous tissue (also sometimes referred to as the hypodermis layer) and muscle tissue, in that order. There is considerable variation in the skin thickness both between individuals and within the same individual at different sites of the body. Generally, the outer skin layer, epidermis, has a thickness between 50-200 microns, and the dermis, the inner and thicker layer of the skin, has a thickness between 1.5-3.5 mm. Therefore, a needle cannula that penetrates the skin deeper than about 3.0 mm has a potential of passing through the dermis layer of the skin and making the injection into the subcutaneous region, which may result in an insufficient immune response, especially where the substance to be delivered intradermally has not been indicated for subcutaneous injection.
The standard procedure for making an intradermal injection via the Mantoux technique is known to be difficult to perform, and therefore dependent upon experience and technique of the healthcare worker. This procedure is recommended to be performed by accessing the vial with the needle and aspirating the medication into the syringe, stretching the skin, orienting the bevel of short bevel needle cannula (in one embodiment, a 26G×½″) upwardly and inserting the needle cannula to deliver a volume of 0.5 ml or less of the substance into the skin of an animal with the needle cannula being inserted into the skin at an angle varying from around 10-15 degrees relative to the plane of the skin to form a blister or wheal in which the substance is deposited or otherwise contained. Accordingly, the technique utilized to perform the standard intradermal injection is difficult and requires the attention of a trained nurse or medical doctor; however this method does have the advantage of allowing the filling of the syringe directly from the vial. FIG. 2 of US Published Application No. 2005-0203459 A1 to Alchas shows a conventional syringe being filled from a multi-dose vial, which demonstrates that the length of the needle must be sufficient to fully penetrate the septum of a vial in order to aspirate the medication. Inserting the needle to a depth greater than about 3.0 mm may results in a failed intradermal injection, as the substance being expelled through the cannula will be injected into the subcutaneous tissue of the animal. Further, the standard method is not suitable for self-administration of intradermal injections. However, this method does have the advantage of being able to use the same needle for penetrating the vial and filling as is used for performing the injection, allowing the practitioner to select a fixed needle, which reduces dead space.
For many drug substances, it may be desirable to fill the delivery device at the point of, and immediately prior to use. In this situation, the delivery device is normally filled from a multi-dose vial. A multi-dose vial may be more economical and it enables the user to fill the delivery device with the specific dose required. The multi-dose vial may be pre-filled with a liquid substance or with a dry substance. For example, it is now conventional to reduce certain drugs to a dry or powdered form to increase the shelf life of drugs and reduce inventory space and pre-fill (or fill at time of use) a syringe with diluent for reconstitution of the dry drug. Multi-dose vials may be sealed with an elastomeric stopper or septum of thickness exceeding 3 mm. Additionally, some vial septums are coated with hard materials like PTFE (e.g. Teflon® PTFE) which could damage the filling needle upon penetration. A needle on the delivery device may be used to pierce the stopper or septum and draw the drug substance from the vial into the delivery device, typically a syringe. The drug substance may then be administered using the delivery device, which is discarded after use, and the unit-dose vial may be stored for further use. One problem with using a short needle which is suitable for intradermal injection is that the needle used for injection, when penetrated into certain vials is not long enough to access the medication within the vial.
Vial adapters to aid in penetration of vials have been proposed in the past. Various designs have been proposed in the past to align the vial to the syringe. One example of such a device is related in U.S. Pat. No. 5,356,406 to Shraga. The design of this adapter is such that it provides guidance of the needle to the vial. The vial adapter of '406 requires the use of a needle of sufficient length to penetrate the septum of the vial. Another such example of a vial adapter is related in U.S. Pat. No. 4,944,736 Holtz. The design of this adapter is such that it provides guidance of the needle to the vial. In addition, the vial adapter of '736 requires the use of a needle of sufficient length to penetrate the septum of the vial.
Further, with the advent of viral infections that are transferred through contact with bodily fluids, it is desirable to enclose or conceal a needle cannula subsequent to administering an injection. Preferably, a delivery device should include a mechanism that is capable of enclosing a needle cannula immediately subsequent to administering the injection. If a needle is left uncovered for even a short period of time after administering an injection, such as, for example, while trying to reattach a needle cap, a biohazard exists. Therefore, it may be desirable to provide an intradermal delivery device with a means for enclosing the needle cannula that is simply designed, easy to use, and readily available immediately after administering an injection.
The use of intradermal delivery systems is expected to increase. Use of a “standard” length needle to deliver a drug substance intradermally has its shortcomings, some of which are identified above. It is not possible to use a delivery device having a needle length suited for intradermal injection to aspirate a syringe with drug substance from a standard multi-use vial. Thus, there are shortcomings in the prior art that prevent filling an intradermal injection using a “short” length needle and a multi-use vial. As a result, there is a need to pre-fill an intradermal device, or to use a “long” detachable needle for filling the device and a “short” detachable needle for the drug administration, resulting in dead space losses. It would be advantageous to have a drug delivery device capable of accessing substances stored in multi-dose vials and delivering such substances into the intradermal region of the skin without encountering the shortcomings described above.